Noise is Difficult to Define

Noise is Difficult to Define - Part 1

Editor: Is it just me or are we suddenly being inundated with articles on noise and its effect on hearing loss? It seems that I see a related article at least once a week! I guess that's good, if it means people are becoming aware of noise's potential to damage hearing. Here's a great article on noise from ASHA (http://www.asha.org/hearing/disorders/noise.cfm).

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People who study acoustics define noise as complex sound waves that are aperiodic, in other words, sound waves with irregular vibrations and no definite pitch.

In engineering, noise is defined as a signal that interferes with the detection of or quality of another signal.

The combined disciplines of psychology and acoustics (psychoacoustics) study the response of humans to sound. They define noise as unwanted sound.

Is music noise? Is the hum of tires on a highway noise? Is the surround-sound movie theater noise? Is the philharmonic concert noise? And what about the accompanying beat for aerobic exercises at the health club? Sounds that are soothing for some are irritating to others.

An expert on noise, K.D. Kryter (1996) in his text, Handbook of Hearing and the Effects of Noise, (New York Academic Press) defined noise as "acoustic signals which can negatively affect the physiological or psychological well-being of an individual."

Basically, noise is unwanted sound. It is a pollutant and a hazard to human health and hearing. In fact, it has been described as the most pervasive pollutant in America.

Noise in our environment affects physical heath. Noise also has psychological and social implications and affects our well being and quality of life.

Unfortunately, public awareness of the hazardous effects of noise is low - especially noise considered to be non-occupational. To this end, the fourth Wednesday in April has been declared International Noise Awareness Day (INAD). As part of International Noise Awareness Day, a "Quiet Diet" is encouraged and is launched by observing 60 seconds of no noise from 2:15 to 2:16 PM. The reduction, if not stopping of everyday noises around us raises our awareness of the impact noise has on health and hearing.

According to the National Institute on Deafness and Other Communication Disorders (NIDCD) http://www.nidcd.nih.gov/ more than 30 million Americans are exposed to hazardous sound levels on a regular basis. Of the 28 million Americans who have some degree of hearing loss, over one-third have been affected, at least in part, by noise.

Damage to the Inner Ear

Your ear receives sound waves and sends them through a delicately balanced system to the brain. Part of this remarkable system, the cochlea, is a chamber in the inner ear filled with fluid and lined with thousands of tiny hair cells. The hair cells signal the auditory nerve to send electrical impulses to the brain. The brain interprets these impulses as sound. When you are exposed to loud or prolonged noise, the hair cells are damaged and the transmission of sound is permanently altered.

Noise Levels

Both the amount of noise and the length of time you are exposed to the noise determine its ability to damage your hearing. Noise levels are measured in decibels (dB). The higher the decibel level, the louder the noise. Sounds louder that 80 decibels are considered potentially hazardous. The noise chart below gives an idea of average decibel levels for everyday sounds around you.

Painful:
150 dB = rock music peak
140 dB = firearms, air raid siren, jet engine
130 dB = jackhammer
120 dB = jet plane take-off, amplified rock music at 4-6 ft., car stereo,
band practice

Extremely loud:
110 dB = rock music, model airplane
106 dB = timpani and bass drum rolls
100 dB = snowmobile, chain saw, pneumatic drill
90 dB = lawnmower, shop tools, truck traffic, subway

Very loud:
80 dB = alarm clock, busy street
70 dB = busy traffic, vacuum cleaner
60 dB = conversation, dishwasher

Moderate:
50 dB = moderate rainfall
40 dB = quiet room

Faint:
30 dB = whisper, quiet library

Warning Signs of Hazardous Noise

a.. You must raise your voice to be heard
b.. You can't hear someone two feet away from you
c.. Speech around you sounds muffled or dull after leaving a noise area
d.. You have pain or ringing on your ears (tinnitus) after exposure to noise.

Hazardous Noise

Sounds louder than 80 decibels are considered potentially dangerous. Both the amount of noise and the length of time of exposure determine the amount of damage. Hair cells of the inner ear and the hearing nerve can be damaged by an intense brief impulse, like an explosion, or by continuous and/or repeated exposure to noise.

Examples of noise levels considered dangerous by experts are a lawnmower, a rock concert, firearms, firecrackers, headset listening systems, motorcycles, tractors, household appliances (garbage disposals, blenders, food processors/choppers, etc.) and noisy toys. All can deliver sound over 90 decibels and some up to 140 decibels.

Can't my ears "adjust" and "get used" to regular noise?

If you think you have "gotten used to" the noise you are routinely exposed to, then most likely you have already suffered damage and have acquired a permanent hearing loss. Don't be fooled by thinking your ears are "tough" or that you have the ability to "tune it out"! Noise induced hearing loss is usually gradual and painless, but, unfortunately, permanent. Once destroyed, the hearing nerve and its sensory nerve cells do not regenerate!

An audiologist certified by the American Speech-Language-Hearing Association (ASHA) can conduct a hearing evaluation to determine if you do have a hearing loss. If you are routinely exposed to noise, you should have your hearing checked by an ASHA-certified audiologist on a regular basis, at least once a year. In almost all states, a license to practice audiology is also required.

Part Two

Part Three